Process for the preparation of angiotensin-II analogues substituted in the 1-, 5- and 8-positions

Abstract

 The invention relates to octapeptides of the formula

wherein

X is a sarcosyl, lactoyl or hydroxyacetyl radical,

Y is cyclopentylglycyl or cyclohexylglycyl, and W is an aliphatic amino acid radical or lactic acid radical, having angiotensin-II antagonistic activity.

A process for their preparation is also disclosed as are compositions containing them.

Description

[0001] The invention relates to a process for preparing new peptides of the formula

[0002] 

wherein

X stands for a sarcosyl, lactoyl or hydroxyacetyl radical,

Y is cyclopentylglycyl or cyclohexylglycyl,

W is an aliphatic amino acid radical or lactic acid radical,

having angiotensin-II antagonistic activity, to the peptides themselves and to pharmaceutical compositions containing them as active ingredient.

[0003] Angiotensin-II (hereafter designated AII), which is liberated from angiotensin-I by the "converting enzyme" angiotensinase, exerts its hypertensive activity in organisms via a double mechanism. On one hand, AII has a direct effect on the involuntary muscles, and as a result of muscle contraction increases the peripheral resistance and thereby the blood pressure. On the other hand, AII increases aldosterone evolution in the adrenal cortex, and the increased aldosterone production, accompanied by sodium and water retention, also results in increased blood pressure.

[0004] AII antagonists are those structural analogues of AII which block the AII receptors in both mechanisms, and in this manner prevent the hormone from exerting its activity.

[0005] Since the synthesis of the first effective analogues (German OLS No. 2,127,393) numerous AII antagonists have been prepared. It has turned out that in the particularly potent antagonists the phenylalanine group in the 8-position is substituted by an amino acid having an aliphatic side- chain. The activity can be increased by incorporating sarcosyl, succinyl, aminooxyacetyl, etc. groups in the 1-position and hydroxyacids in the 8-position (German OLS Nos. 2,758,483, 2,602,803, 2,846,200 and Hungarian Patent Specifications Nos. 177,133, 177,134 and 181,008).

[0006] These modifications resulted in active AII antagonists but up to the present only one AII analogue ([Sar^l,Va1⁵,Ala⁸]-ArI analogue, Saralasin ) has been placed on the market for diagnostic use. Wider use of AII antagonists is prevented by their short duration of activity, and also by the fact that the hitherto synthesized analogues without exception have a temporary agonistic acitivty as well (Fed. Proc., 35, 2486 (1976)). For example [Sar¹, Thr(OMe)⁸]-AII, which is a potent antagonist (US Patent No. 3,976,770) induced an initial 1.7 to 2.0 kPa (13 to 15 mmHg) increase in blood pressure in in vivo experiments (J. Med.Chem., 20, 1051 (1977)). On the other hand, the analogues with no or little temporary agonistic effect proved to be poor antagonists. For example, [Sar¹,Thr⁸]-AII has a small agonistic acitivity but shows no aldosterone release inhibiting effect [Eur. J. Clin. Pharm., 23, 7 (1982)]. Hence, no AII analogue has yet been synthesised with both a remarkable antagonistic acivity and at the same time little or no temporary agonistic activity.

[0007] We have found that by replacing the isoleucine in the 5-position by cyclohexylglycine or cyclopentyl- glycine, AII inhibitors are obtained, which have a remarkable, prolonged hypotensive activity, the most potent aldosterone release inhibiting activity of the hitherto known antagonists, and a low temporary agonistic activity.

[0008] According to one aspect of the invention, novel octapeptides of the formula

are prepared by reacting a novel protected octapeptide of the formula

wherein

Y and W are as defined above, and Z is a protecting group removable by acidolysis or catalytic hydrogenation, preferably benzyloxycarbonyl or tert.- butoxycarbonyl,

A is a group suitable for the temporary protection of the guanidino group of arginine, preferably a nitro group,

B is a group suitable for the temporary protection of the aromatic hydroxyl group of tyrosine, preferably benzyl or substituted benzyl,

E is a group suitable for the temporary

protection of the imidazole group of histidine, preferably dinitrophenyl,

C is a group suitable for the temporary protection of the C-terminal carboxyl group, resistant to acid treatment but removable for example by catalytic hydrogenation, for example benzyl or substituted benzyl, and

X' depending on the meaning of X, represents either a sarcosyl group or an aliphatic carboxylic acid radical containing an aminooxy group in the o-position,

[0009] with a thiol to yield a novel protected octapeptide of the formula

which is then subjected to conditions of catalytic hydrogenolysis.

[0010] During this treatment, if X¹ is an o-aminooxy-acid radical, the corresponding octapeptide of the formula (I), in which X stands for an alpha- hydroxyacid, is obtained in a single step, due to the splitting of the N-O bond (see Hungarian Patent Specification No. 177,133).

[0011] In the process of the invention, the peptides of formula (II) will preferably be prepared using the active ester technique, building up from the C-terminal acid.

[0012] The octapeptides of the formula (I) may be purified in a manner known per se, preferably by cellulose ion exchange chromatography. As a result, compounds are generally obtained as lyophilized powders, which can be converted into the corresponding acid addition salts or complexes.

[0013] According to a further aspect of the invention we provide a process for the preparation of pharmaceutical compositions containing as active ingredient an octapeptide of the formula

wherein X, Y and W are as hereinbefore defined, which comprises converting an octapeptide of the formula (I) into pharmaceutical compositions, using carriers, excipients and formulation aids conventionally used in the preparation of pharmaceutical compositions.

[0014] According to still further aspects of the invention we provide novel octapeptides of formula I as hereinbefore defined, novel protected octapeptides of formulae II and III as hereinbefore defined and pharmaceutical compositions containing an octapeptide of formula I as hereinbefore defined.

[0015] The inhibiting effect of the compounds of the formula (I) on aldosterone production and vasoconstriction was tested in in vitro experiments. In these tests the inhibition of vasoconstriction induced by AII was measured on isolated rabbit aorta vessel preparate [J. Pharmacol. Exp. Ther., 108, 129 (1953)]. The results obtained are shown in Table 1 on the following page (in pA₂).

[0016] The aldosterone production inhibiting activity is also shown in Table 1.

[0017] Though Sar¹,HMV⁸-AII used as a control possesses a strong aldosterone production inhibiting activity, its pharmacological application is limited by the fact that when administered in a 10 pg/kg dose, it shows a 2.6 kPa (19.6 mmHg) initial hypertensive activity.

[0018] The results set forth in Table 1 show that certain representatives of the new analogues according to the invention show essentially the same aldosterone production inhibiting activity as the control compounds, while others are more potent.

[0019] The hypotensive activity of the new compounds was tested in vivo on awake rats, according to the

modified method of Pals [Circ. Res. 29, 664 (1971) 7.

[0020] The results are illustrated on Figure 1.

[0021] At first a dose - effect curve was registered for AII on rats. The peptides were administered subcutaneously, in 1 mg/kg doses. In the fifth minute after administration and repeatedly in the next three hours 1.0 _/ug/kg of AII was added intravenously. The statistical evaluation was performed. by variancy analysis.

[0022] The results illustrated by the Figure show that of the new analogues [Sar¹,Chg⁵,Ala⁸]-AII and [Sar¹,Chg⁵,Lac⁸]-AII on awake rats have a singifi- cantly more prolonged hypotensive activity than Saralasin used as a control.

[0023] The temporary hypertensive activity of the AII analogues was also tested on awake rats. AII analogues were administered into the jugular vein every 2₀ minutes. The results were evaluated by variancy analysis. The comparative results obtained on [Sar¹,Chg⁵,Lac⁸]-AII are shown on Figure 2.

[0024] According to the data illustrated on the Figure this analogue has a significantly lower initial hypertensive activity than Saralasin used as a control substance.

[0025] The invention will now be illustrated in greater detail by the following non-limiting Examples.

[0026] The abbreviations used in the specification are symbols generally accepted in the art [J. Biol. Chem. 247, 977 (1972)_7. For the abbreviation of alpha-amino-oxyacids the symbol "0" has been employed together with the symbol of the corresponding amino acid (e.g. OGly = alpha-aminooxy-acetic acid).

[0027] During the preparation of the compounds the solvent was eliminated in a Rotavapor equipment (Büchi). Melting points were determined in a Dr. Tottoli's equipment. For thin layer chromatography Kieselgel 60 F₂₅₄ plates (Merck) were used and the chromatograms were developed in the following solvent mixtures, where the ratios are indicated by volumes.

The thin layer chromatograms were developed with ninhydrin, or,after chlorination, with o-toluidine + potassium iodide solution.

[0028] R_f values are shown as R_f^n-where n indicates one of the solvent mixtures above.

[0029] The optical rotation was determined using a Perkin-Elmer 141 polarimeter.

[0030] The end product was purified by dissolving 0.5 g of free peptide in 4 ml of a 0.01 molar ammonium acetate solution, and pouring the solution onto a column filled with 0.5 ml of carboxymethyl cellulose (CMC 52), which had previously been equilibrated with the above buffer. By combining 0.01 molar and 0.5 molar ammonium acetate solutions with a gradient stirrer, gradient elution is carried out for 4 days, at a flow rate of 25 ml/hour. The eluate discharged from the column is continuously monitored by an LKB Uvicord-II, whereupon on the basis of the curve obtained, the main fraction is lyophilized.

[0031] Boc-Chg-OPfp and Boc-Cpg-OPfp used for the synthesis are new compounds:

Melting point: 91 to 94 °C and 98 to 99 °C, respectively; [α]²⁴_D= -20.2 ^° and -31.8°, respectively.

Example 1

[0032] 

2.0 g (8 mmoles) of Ala-ONB.HCl are dissolved in 30 ml of chloroform, and 1.12 ml of triethyl amine and 1.52 g (4 mmoles) of Boc-Pro-OPfp are added. After stirring at room temperature for 30 minutes, the solution is shaken with water and with a 10 % citric acid solution. After drying and evaporation the protected dipeptide (R_f¹=₀.7) is dissolved in 8 ml of a 8 N solution of hydrochloric acid in dioxane, without isolation, after 15 ml the solution is diluted with dry ether and evaporated. The free dipeptide hydrochloride (R_f⁴=0.65) is dissolved in 20 ml of dimethyl formamide, the pH is adjusted to 8 with triethyl amine, and 3.52 g (6 mmoles) of Boc-His(Dnp)-OPfp are added. After stirring for 30 minutes the solvent is eliminated, the oily residue is dissolved in 50 ml of ethyl acetate, and 0.88 ml of N,N-dimethylamino-ethylamine are added. After 15 minutes the solution is shaken with a 10 % citric acid solution, 1 N hydrochloric acid, water and 5 % sodium bicarbonate solution. After drying and evaporation the oily residue is solidified with 30 ml of ether, the precipitate is filtered off and washed with vether. 2.5 g (88 %) of the protected tripeptide are obtained, R_f²=₀.6₀.

[0033] 1.0 g (1.42 mmoles) of Boc-His(Dnp)-Pro-Ala-ONB obtained are dissolved in 6 ml of a 8 _N solution of hydrochloric acid in dioxane, whereupon after 15 minutes the free tripeptide hydrochloride (R_f³=0.30) is precipitated with dry ether, filtered and washed with ether. It is immediately dissolved in 10 ml of dimethyl formamide, the pH is adjusted to 8 with triethyl amine, and 0.86 g of Boc-Chg-OPfp are added. After 30 minutes the reaction mixture is evaporated, the residue is dissolved in 30 ml of ethyl acetate and it is shaken with a 10 % aqueous citric acid solution, water and subsequently a 5 % sodium bicarbonate solution. After drying and evaporation the protected tetrapeptide (R_f²=0.8) is solidified with 50 ml of n-hexane, filtered and washed with n-hexane. Thereafter, it is dissolved in 6 ml of a 8 N solution of hydrochloric acid in dioxane, and after 15 minutes the free tetrapeptide hydrochloride (R_f³=₀.20) is precipitated with dry ether, filtered and washed with ether. The product is immediately dissolved in 10 ml of dimethyl formamide, the pH is adjusted to 8 with triethyl amine, and 0.8 g (1.5 mmoles) of Boc-Tyr(Bzl)-CPfp are added. After 30 minutes the solvent is replaced by ethyl acetate, 0.11 ml of dimethylaminoethyl amine are added, and after 15 minutes the mixture is shaken with a 1 _N hydrochloric acid solution, water and subsequently a 5 % sodium bicarbonate solution. After drying and evaporation the protected pentapeptide (R_f¹=0.35) is solidified with 30 ml of ether, filtered and washed with ether. It is then dissolved in 10 ml of a 8 N solution of hydrochloric acid in dioxane, after 10 minutes the free pentapeptide hydrochloride (Rf3=O.35) is precipitated with dry ether, filtered and washed with ether. It is immediately dissolved in 15 ml of dimethyl formamide, the pH is adjusted to 8 with triethyl amine, and 0.75 g (2 mmoles) of Boc-Val-OPfp are added. After stirring for 30 minutes the solvent is exchanged for chloroform, and it is shaken with a 10 % citric acid solution, 1 N hydrochloric acid and water. After drying and evaporation the protected hexapeptide (R_f¹=0.37) is solidified, filtered and washed with ether. Thereafter, the product is dissolved in 20 ml of a 8 N solution of hydrochloric acid in dioxane, and after 15 minutes the free hexapeptide hydrochloride (R_g⁴=0.45) is precipitated with dry ether, filtered and washed with ether. It is immediately dissolved in 15 ml of dimethyl formamide, the pH is adjusted to 8 with triethyl amine, and 0.98 g (2.0 mmoles) of Boc-Arg(NO₂)-0Pfp are added. After stirring for one hour, the solution is diluted with 45 ml of chloroform, and shaken with a 10 % citric acid solution, 1 N hydrochloric acid and subsequently with water. The residue obtained after drying and evaporation is solidified with ethanol, and filtered (R_f²=0.30). The protected heptapeptide is dissolved in 20 ml of a 8 _N solution of hydrochloric acid in dioxane, and after 20 minutes the free heptapeptide hydrochloride (R_f³=0.2₁) is precipitated by adding dry ether, filtered, washed and immediately dissolved in 15 ml of dimethyl formamide. The pH of the solution is adjusted to 8 with triethyl amine, and there are added 0.59 g (1.5 mmoles) of Z-Sar-OPfp. After one hour, the reaction mixture is evaporated, and the oily residue is solidified with 15 ml of ethanol, filtered, and washed with ethanol and'.then with ether. 1.5 g (70 %, related to Boc-His(Dnp)-Pro-Ala-ONB) of the title compound are obtained. Melting point: 194 °C (decomposition); R_f²=0.4, _Rf³₌₀.80.

Example 2

H-His(Dnp)-Pro-Lac-OBzl.HCl

[0034] 7.3 g (30 mmoles) of lactic acid zinc salt are suspended in 40 ml of dimethyl formamide, and to the suspension 4.2 ml (30 mmoles) of triethyl amine and 0.36 g (30 mmoles) of Boc-Pro-OSu are added. After stirring for 24 hours at room temperature the solution be.comes clear. Thereafter, dimethyl formamide is eliminated under reduced pressure, the residue is dissolved in 150 ml of ethyl acetate, and it..is shaken with 1 _N hydrochloric acid and subsequently water. After drying and evaporation Boc-Pro-Lac-OH is solidified with 50 ml of hexane and filtered. The crude product is recrystallized from a 1:1 mixture of ether and hexane (40 ml) to yield 6.6 g (77 %) of the title compound. Melting point: 108 to 110 °C, [α]²⁴_D=-88.2° (c=₂, ethanol), _Rf⁵₌0.30.

[0035] 2.87 g (10 mmoles) of Boc-Pro-Lac-OH obtained are dissolved in 20 ml of ethyl acetate, whereupon 1.7 ml (12 mmoles) of triethyl amine and 1.42 ml (12 mmoles) of benzyl bromide are added. The solution is refluxed for 8 hours, and then it is diluted with 20 ml of ethyl acetate, and shaken with water, 1 N hydrochloric acid and a 5 % sodium bicarbonate solution. After drying and evaporation Boc-Pro-Lac-OBzl is obtained as an oily product. Yield: 3.05 g (81 %), R_f¹=0.67, [α]²⁴_D = -90.0° (c=2, ethanol).

[0036] 2.65 g (7.0 mmoles) of Boc-Pro-Lac-OBzl are dissolved in 10 ml of a 8 N solution of hydrochloric acid in dioxane. After 15 minutes the solution is diluted with dry ether and evaporated. H-Pro--Lac-OBzl hydrochioride (R_f⁴=0.2) obtained is dis- solved in 15 ml of dimethyl formamide, the pH of the solution is adjusted to 8 with triethyl amine, and 3.5 g (6 mmoles) of Boc-His(Dnp)-OPfp are added. After stirring for one hour, dimethyl formamide is evaporated, the residue is dissolved in 60 ml of ethyl acetate and shaken with a 1 N hydrochloric acid solution, water and subsequently a 5 % sodium bicarbonate solution. After drying and evaporation an oily residue is obtained, which is dissolved in 15 ml of a 8 N solution of hydrochloric acid in dioxane, and after 15 minutes the free tripeptide hydrochloride (R_f³=0.10) is precipitated, filtered and washed with ether. Yield: 2.8 g (78 %).

[0037] The peptide chain is built up further as described in Example 1. Further AII analogues prepared in an analogeous manner are shown in Table 2.

Example 3

Elimination of the protecting groups

[0038] 1.5 g (1 mmoles) of Z-Sar-Arg(NO₂)-Val-Tyr(Bzl)-Chg-His(Dnp)-Pro-Ala-ONB are dissolved in 5 ml dimethyl formamide, 1.9 ml (25 mmoles) of 2-mercaptoethanol are added, and after stirring for one hour, the product is precipitated with dry ether, filtered and washed with ethanol. 1.23 g (91 %) of Z-Sar--Arg(NO₂)-Val-Tyr(Bzl)-Chg-His-Pro-Ala-ONB are obtained. _Rf²₌0.20, R_f³₌o.40. The material is dissolved in a 5:1:1 (by volume) mixture of methanol, acetic acid and water, 0.6 g of a 10 % palladium-on-charcoal catalyst are added, and hydrogen gas is bubbled through the mixture with stirring for 25 hours. The progress of the reaction is monitored by thin layer chromatography to determine the end-point. the catalyst is then filtered off, and the solution is evaporated to dryness. To the residue a 9:1 mixture (by volume) of ethanol and water is added, it is evaporated and the residue is solidified with ethanol, filtered and washed with

[0039] ethanol. 0.7 g (74 %) of Sar¹,Chg⁸,Ala⁸-AII are obtained. The product is purified as described above. R_f⁵=0.10, R_f⁶=0.27, [α]²⁴_D=-84.50 (c=0.3, 1m AcOH). Amino acid analysis:Pro1(1), Ala 1.15 (1), Val 0.95,(1),

[0040] His 0.85(1), Tyr 0.86 (1).

[0041] Further free octapeptides prepared in an analogous manner are disclosed in Table 3.

Claims

1. A process for the preparation of new peptides of the formula

wherein

X is a a sarcosyl, lactoyl or hydroxyacetyl radical,

Y is cyclopentylglycyl or cyclohexylglycyl, and

W is an aliphatic amino acid radical or lactic acid radical,

having angiotensin-II antagonistic activity, which comprises reacting a protected octapeptide of the formula

wherein

Y and W have the same meaning as defined above, and

Z is a protecting group removable by acidolysis or catalytic hydrogenation,

A is a group suitable for the temporary protection of the guanidino group of arginine,

B is a group suitable for the temporary protection of the aromatic hydroxyl group of tyrosine,

E is a group suitable for the temporary protection of the imidazole ^qrou^p of histidine,

G is a group suitable for the temporary protection of the C-terminal carboxyl group, resistant to acid treatment

but removable by catalytic hydrogenation, and X depending on the meaning of X, represents either a sarcosyl group or an aliphatic carboxylic acid radical containing an aminooxy group in the o-position,

with a thiol to yield a protected octapeptide of the formula

wherein Z, X', A, B, Y, W and G are as defined above, which is then subjected to conditions of catalytic hydrogenolysis.

2. A process as claimed in claim 1 wherein Z is selected from benzyloxycarbonyl or t.butoxycarbonyl, and/or A is a nitro group, and/or B is selected from a benzyl or substituted benzyl group, and/or E is a dinitrophenyl group and/or G is selected from a benzyl or substituted benzyl group.

3. A process as claimed in claim 1 or claim 2 wherein the peptide of formula (II) is prepared using an active ester technique building up from the C-terminal acid.

4. A process as claimed in any of claims 1 to 3 for the preparation of peptides of the formula (I), in which Y is a cyclopentylglycyl group and X and W are as defined in claim 1, which comprises building up a protected octapeptide of the formula (II), in which Y is a cyclopentylglycyl group and _Z, _X¹, A, _B, _E, _W and G are as defined in claim 1, and reacting the obtained product with a thiol, and subjecting the protected octapeptide of the formula (III) obtained, in which Z, x^l, A, B, Y, W and G are as defined above, to catalytic hydrogenation.

5. A process as claimed in any of claims 1 to 3 for the preparation of peptides of the formula (I), in which Y is a cyclohexylglycyl group and X and W are as defined in claim 1, which comprises building up a protected octapeptide of the formula (II), in which Y is cyclohexylglycyl and Z, X¹, A, B, E, W and G are as defined in claim 1, reacting the product obtained with a thiol, and subjecting the protected octapeptide of the formula (III) obtained, wherein Z, X¹, A, B, Y, W and G are as defined above, to catalytic hydrogenation.

6. A process as claimed in any one of claims 3 to 5 wherein the active esters used are pentafluorophenyl esters.

7. A process as claimed in any one of claims 1 to 6 wherein the thiol used for the elimination of the protecting group E is 2-mercaptoethanol.

8. A process as claimed in any one of claims 1 to 7, wherein the catalytic hydrogenation is effected using a palladium-on-charcoal catalyst.

9. A process for the preparation of pharmaceutical compositions containing as active ingredient an octapeptide of the formula

wherein X, Y and W are as defined in claim 1, which comprises converting an octapeptide of the formula (I), wherein X, Y and W are as defined above, prepared according to any one of claims 1 to 6, into pharmaceutical compositions, using carriers, excipients and formulation aids conventionally used in the preparation of pharmaceutical compositions.

10. Octapeptides of the formula (I), in which X, Y and W are as defined in claim 1 or claim 2.

11. Protected octapeptides of the formula (II) wherein _Z, X¹, A, B, Y, E, W and G are as defined in claim 1 or claim 2.

12. Protected octapeptides of the formula (III) wherein _Z, _X¹, A, _B, Y, W and G are as defined in claim 1 or claim 2.

13. Pharmaceutical compostions containing as active ingredient an octapeptide of the formula (I).

14. Use of a compound of formula (I) in the treatment or prophylaxis of hypertensive states.

15. Reactive peptide esters of the formula

wherein Boc is benzyloxycarbonyl, Y is cyclohexylglycyl or cyclopentylglycyl and Pfp is a pentafluorophenyl group.

Drawing